The invention relates to a chucking fixture for a tool or a workpiece, comprising a chuck and a toolholder or workholder matching the chuck, the chuck having posts having bearing surfaces for orienting the tool or workpiece in an X and Y direction and having end faces for establishing a plane perpendicular to the Z direction.
In machine tool building, chucking fixtures are used to secure tools and/or workpieces at a precisely defined position in an X-Y-Z coordinate system. The tool is, for example, an electrode used in a vertical eroding system to machine a workpiece by means of spark erosion. The tool, in this case for example the electrode, is inserted in a toolholder which is received by a matching chuck. In the manufacture of molds for injection-molded products in which high requirements are placed on dimensional precision, at least as high requirements are placed on the precision of the injection molds. The reproducibility of the clamping process of the different tools which are used in the course of the machining and of the workpieces also has an influence on the dimensional precision and on the appearance of the product. Conventional commercial chucking fixtures achieve positional precision of +/−2 μm.
A generic chucking fixture is known from EP 255 042 B1. The chucking fixture has, arranged at right angles to each other, two pairs of grooves and two pairs of strips having resilient lips. The chucking fixture is used, for example, to clamp the electrode in a vertical erosion system.
A device for absolute distance measurement is known from DE 195 28 676 C2. The device comprises an optical interferometer having optical fibers, with two lasers as light sources, the wavelength of at least one laser being tunable, with beam splitters, photoelectric receivers and with a computer for evaluating the signals and for calculating the distance with a precision in the nanometer range.
It is the object of the invention to provide a chucking fixture which allows precise and reproducible clamping in the nanometer range and takes up as little space as possible in the machining system.
The object is achieved by providing a chucking fixture for a tool or a workpiece, comprising a chuck and a toolholder or workholder matching the chuck, the chuck having posts having bearing surfaces for orienting the tool or workpiece in an X and Y direction and having end faces for establishing a plane perpendicular to the Z direction, devices for measuring the distance between the chuck and the toolholder or workholder being formed in the bearing surfaces and in the end faces.
It is advantageous that the chucking fixture, at a precision in the nanometer range, takes up as little space as possible in the machining system. This is achieved as a result of the fact that the devices for measuring the distance are formed as optical interferometers.
It is also advantageous that the chucking fixture can be used to measure, in addition to the absolute distance measurement, also forces such as, for example, torsional forces or vibrations. This is achieved as a result of the fact that the optical interferometers are coupled to an electronic evaluation system.
It is furthermore also advantageous that the chucking fixture can be used to measure the change in dimension as a result of the change in temperature. This is achieved as a result of the fact that the optical interferometers are arranged on opposing bearing surfaces and/or end faces of the chucks and/or toolholders. A measuring device on two opposing sides of a groove or a strip of the chucking fixture increases the reliability of the measurement and allows thermal expansion to be corrected.
The core idea of the invention is to have contactless measurement integrated in the chucking fixture of a vertical erosion system. If the measuring device is integrated in the chucking fixture, external measurements on the clamped tool or workpiece are dispensed with. The measured values obtained by the electronic evaluation system can be used to correct the position of the chucking fixture. This saves time for clamping and unclamping and greatly improves the precision of the positioning.